Process for producing a carboxylic acid ester by reacting an aldehyde and an alcohol using a palladium type catalyst

ABSTRACT

A carboxylic acid ester is prepared by a process comprising: 
     reacting an aldehyde and an alcohol in a liquid phase in the presence of molecular oxygen as indicated by the following reaction: 
     
       
         RCHO+R′OH+O 2 →RCOOR′+H 2 O 
       
     
     in the presence of a catalyst comprising at least palladium and an element X, wherein X is bismuth, lead or a combination thereof, supported on a carrier, wherein the catalyst has an acid strength, pKa, of more than 4.8 and shows an ammonia chemical adsorption amount at 0° C. of 0-150 μmol/g-catalyst.

TECHNICAL FIELD

The present invention relates to a process for producing a carboxylicacid ester by reacting an aldehyde and an alcohol in a liquid phase inthe presence of molecular oxygen by using a catalyst and to a catalystused for the process.

BACKGROUND ART

Catalysts which have been proposed to be used in a process for producinga carboxylic acid ester from an aldehyde and an alcohol in the presenceof molecular oxygen by using a catalyst include, for example, apalladium-lead type catalyst disclosed in JP-B-57-35856, JP-B-4-72578,JP-A-57-50545 and others, a palladium-tellurium type catalyst disclosedin JP-A-61-243044, a palladium-thallium-mercury type catalyst disclosedin JP-B-57-35860, a palladium-alkaline earth metal-zinc-cadmium typecatalyst disclosed in JP-B-57-19090, and a palladium-bismuth typecatalyst disclosed in JP-B-61-60820, JP-B-62-7902, JP-A-5-148184 andothers. As to the carrier of the catalyst used for such processes, therehave been proposed, for example, calcium carbonate in JP-B-57-35856 andJP-B-57-35860, zinc oxide-alumina, titania-lanthanum oxide and zincoxide-titania in JP-B-4-46618, zinc oxide in JP-B-4-72578, a carrierhaving a specific surface area of not more than 70 m²/g in JP-A-57-50942and a hydrophobic carrier in JP-A-5-148184.

However, these catalysts are apt to differ in the yield of carboxylicacid esters even when the components and/or the carrier of the catalystare of the same composition. Therefore, the development of a process,improved in the above-mentioned point, which can produce carboxylic acidesters with a high yield has been eagerly awaited.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a process forproducing a carboxylic acid ester from an aldehyde and an alcohol with ahigh yield and a catalyst used for the process.

Thus, the present invention provides a process for producing acarboxylic acid ester, comprising reacting an aldehyde and an alcohol ina liquid phase in the presence of molecular oxygen by the use of acatalyst comprising at least palladium and X (X represents bismuthand/or lead) supported on a carrier, wherein the catalyst used has anacid strength, pKa, of more than 4.8 and shows an ammonia chemicaladsorption amount at 0° C. of 0-150 μmol/g-catalyst.

The present invention further provides a catalyst used for producing acarboxylic acid ester by reacting an aldehyde and an alcohol in a liquidphase in the presence of molecular oxygen, which comprises at leastpalladium and X (X represents bismuth and/or lead) supported on acarrier, has an acid strength, pKa, of more than 4.8 and shows anammonia chemical adsorption amount at 0° C. of 0-150 μmol/g-catalyst.

In the catalyst and the process according to the present invention, thealdehyde used as a starting material may be, for example, aromaticaldehydes, such as benzaldehyde, methylbenzaldehyde, andnitrobenzaldehyde, saturated aliphatic aldehydes, such as acetaldehyde,propionaldehyde and isobutyl aldehyde, and unsaturated aliphaticaldehydes, such as acrolein, methacrolein and crotonaldehyde. Thealcohol of a starting material may be, for example, methanol, ethanol,isopropanol, allyl alcohol and methallyl alcohol.

The catalyst of the present invention and the catalyst used in theprocess of the present invention comprise palladium, as a catalystcomponent, supported on a carrier and additionally bismuth and/or lead,as a catalyst component(s), supported on the carrier. The term“catalyst” herein refers not only to the catalyst components supportedon a carrier but also to the whole catalyst system including thecarrier. A starting material for palladium used in preparing thecatalyst may be, for example, palladium acetate, palladium chloride,palladium nitrate, palladium ammonium chloride, and palladium-amminecomplex salt, a starting material for bismuth may be, for example,bismuth acetate, bismuth carbonate, bismuth chloride, bismuth nitrateand bismuth sulfate, and a starting material for lead may be, forexample, metal compounds, such as lead acetate, lead carbonate, leadchloride, lead nitrate, lead sulfate, lead tartrate and lead citrate.Besides palladium, bismuth and lead, third components, such as chromium,iron, cobalt, zinc, barium and silver, may be supported as catalystcomponents on the carrier. The catalyst components are present on thecarrier in the form of a metal and/or a metal compound.

In the catalyst of the present invention and the catalyst used in theprocess of the present invention, the amounts of the respective catalystcomponents to be supported on the carrier are, based on 100 parts byweight of the carrier, preferably 1-15 parts by weight, more preferably3-13 parts by weight for palladium, and 0.1-15 parts by weight, morepreferably 0.5-12 parts by weight for X. When the catalyst component isa metal compound , the above-mentioned amount to be supported iscalculated in terms of the weight of the metal atom in the metalcompound. The carriers may be for example, calcium carbonate, zincoxide, silica and silica-magnesia. Average particle diameter andspecific surface area of the carrier are, for example, 5-150 μm and50-200 m²/g, respectively.

The catalyst of the present invention and the catalyst used in theprocess of the present invention have an acid strength, pKa, of morethan 4.8. The acid strength, pKa, herein is an index which indicates thedegree of acidity of the surface of a material. It is signified that thelarger the value of pKa, the weaker the acidity. The acid strength pKais determined according to the method described in Shokubai (catalyst),vol. 11 pp. 210-216 (1969) (written by Isao Matsuzaki et al., publishedby Shokubai Gakkai (Catalyst Society)) by using an indicator whichchanges its color in a predetermined range of pKa. When a catalyst whichhas a pKa of not more than 4.8 is used, by-products such as acetals tendto be formed markedly to lower the yield of the carboxylic acid ester ofthe objective product.

The catalyst of the present invention and the catalyst used in theprocess of the present invention show an ammonia chemical adsorptionamount at 0° C. (hereinafter referred to simply as “ammonia chemicaladsorption amount”) of 0-150 μmol/g-catalyst, preferably 30-140μmol/g-catalyst. The term “ammonia chemical adsorption amount”hereinrefers to the amount of ammonia chemically adsorbed to 1 g of catalystat 0° C. It is signified that the larger the value of theabove-mentioned amount, the larger the amount of acid sites per 1 g ofthe catalyst (hereinafter referred to as “acid amount”). To determinethe ammonia chemical adsorption amount, the total adsorption amount,which is the sum of the chemical adsorption amount and the physicaladsorption amount of ammonia, and the physical adsorption amount ofammonia are determined at 0° C. by using a common adsorption-desorptionapparatus available on the market, and the “ammonia chemical adsorptionamount” can be obtained from the difference of the two amountsdetermined above. When a catalyst which shows an ammonia chemicaladsorption amount of more than 150 μmol/g-catalyst is used, by-products,such as acetals, tend to be formed markedly, to lower the yield of theobjective product.

The catalyst of the present invention and the catalyst used in theprocess of the present invention can be prepared by conventionalmethods. As an example of the method of preparation, the preparation ofa catalyst comprising palladium, bismuth and iron supported on asilica-magnesia carrier is described below. First, palladium chloride,bismuth nitrate and nitric acid are added to water, and the resultingmixture is heated to form a solution. Then, silica-magnesia powder, andthereafter a reducing agent such as formalin are added to the solution,and the resulting mixture is stirred with heating for a predeterminedtime. Thereafter, the mixture is filtered and the solid obtained isimmersed in an aqueous solution of ferric nitrate. In this time, ifdesired, the solid may be reduced again with a reducing agent to deposita metal. The solid is again collected by filtration, and then dried toobtain a catalyst. The catalyst obtained may also be activated byconventional methods.

In the present invention, a carboxylic acid ester is produced byreacting an aldehyde and an alcohol in a liquid phase in the presence ofmolecular oxygen by using a catalyst which has an acid strength, pKa, ofmore than 4.8 and shows an ammonia chemical adsorption amount of 0-150μmol/g-catalyst. The molar ratio of the aldehyde to the alcohol of thestarting materials is preferably 1:100 to 1:1, more preferably 1:80 to1:3.

In carrying out the reaction according to the process of the presentinvention, the catalyst is dispersed as a suspension in the liquidphase. The reaction may be conducted either batch-wise or semibatch-wiseor continuously. The source of the molecular oxygen used as theoxidizing agent may be air, oxygen-enriched air, oxygen or the like. Thereaction temperature is preferably 0-100° C., more preferably 30-80° C.The reaction may be conducted at ordinary pressure or under appliedpressure.

The molecular oxygen is used in an amount sufficient to form theintended carboxylic acid ester. The amount is preferably 10-500 ml/minrelative to 100 ml of the reaction liquid. As to a solvent used forforming the liquid phase, for example, the aldehyde and/or the alcoholused in the process of the present invention may be used as such to formthe liquid phase, but the solvent is not limited thereto. For example,hexane, acetone, benzene and the like may be used as the solvent. Theamount of the catalyst to be used is not particularly limited, and maybe, for example, 0.01 g-1 g per 1 g of aldehyde.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below with reference toExamples and Comparative Examples, but the invention is in no waylimited thereto. The “supported amount” of the metal and/or metalcompound of the catalyst component refers to the weight of metal atom inthe catalyst component, which is a value obtained by calculation fromthe amount of the starting material used for catalyst preparation. Thecatalyst composition was expressed by describing, behind the atomicsymbol of the catalyst component, a supported amount per 100 parts byweight of the carrier and then, behind the slant line (/), the carrier.The acid strength, pKa, was determined according to the method describedin Shokubai, Vol. 11, pp. 210-216 (1969) as mentioned above. The ammoniachemical adsorption amount at 0° C. was determined by using a BET typeadsorption measuring apparatus. Analysis of a reaction product was madeby means of gas chromatography. Conversion of the aldehyde of thestarting material (hereinafter referred to as “conversion”), selectivityto the carboxylic acid ester of the objective product (hereinafterreferred to as “ester selectivity”), selectivity to the acetal ofby-product (hereinafter referred to as “acetal selectivity”) and yieldof the carboxylic acid ester of the objective product (hereinaftereferred to as “yield”) were calculated according to the followingdefinitions,

Conversion (%) = B/A × 100 Ester selectivity (%) = C/B × 100 Acetalselectivity (%) = D/B × 100 Yield (%) = C/A × 100

wherein A, B, C and D respectively represent:

A: the number of moles of fed starting material aldehyde,

B: the number of moles of reacted starting material aldehyde,

C: the number of moles of formed carboxylic acid ester,

D: the number of moles of formed acetal.

EXAMPLE 1

In 50 ml of pure water was dissolved with heating 0.85 g of palladiumchloride, 0.46 g of bismuth nitrate and 5 g of a 60 wt % aqueous nitricacid solution, then 10 g of a silica-magnesia powder with an averageparticle diameter of 100 μm was added to the solution, and the resultingmixture was stirred. To the mixture was added 50 ml of an aqueoussolution containing 5 wt % of sodium hydroxide and 5 wt % of formalin,the resulting mixture was stirred at 70° C. for 30 minutes, thenfiltered, and the resulting cake was washed with water and dried toobtain a catalyst shown in Table 1. In a 300 ml flask fitted with areflux condenser were placed 2 g of the catalyst obtained above, 4.3 gof benzaldehyde and 80 g of methanol, and the mixture was allowed toreact at 50° C. for 2 hours while air was being blown thereinto at aflow rate of 100 ml/min, to obtain methyl benzoate as a carboxylic acidester. The results thus obtained are shown in Table 2.

EXAMPLE 2

In 50 ml of pure water were dissolved with heating 0.85 g of palladiumchloride, 0.46 g of bismuth nitrate and 5 g of a 60 wt % aqueous nitricacid solution, then 10 g of a silica-magnesia powder with an averageparticle diameter of 100 μm was added to the solution, and the resultingmixture was stirred. To the mixture was added 50 ml of an aqueoussolution containing 5 wt % of sodium hydroxide and 5 wt % of formalin,the resulting mixture was stirred at 70° C. for 30 minutes, thenfiltered, and the resulting cake was washed with water (solid A). Thesolid A was added to a solution of 0.72 g of ferric nitrate dissolved in40 ml of pure water, and the mixture was stirred. Then 20 ml of a 5 wt %aqueous formalin solution was added to the mixture, the resultingmixture was filtered, and the cake obtained was washed with water anddried to obtain the catalyst shown in Table 1. A reaction was conductedusing the catalyst under the same conditions as in Example 1, to obtainthe results shown in Table 2.

EXAMPLE 3

A catalyst was prepared in the same manner as in Example 2 except forusing 0.34 g of zinc acetate in place of ferric nitrate, to obtain acatalyst shown in Table 1. The catalyst was used to conduct a reactionunder the same conditions as in Example 1, to obtain the results shownin Table 2.

EXAMPLE 4

In 50 ml of pure water were dissolved with heating 0.85 g of palladiumchloride, 0.16 g of lead nitrate and 2 g of a 60 wt % aqueous nitricacid solution, then 10 g of a silica-magnesia powder with an averageparticle diameter of 100 μm was added to the solution, and the resultingmixture was stirred. To the mixture was added 50 ml of an aqueoussolution containing 5 wt % of sodium hydroxide and 5 wt % of formalin,the resulting mixture was stirred at 80° C. for 30 minutes, thenfiltered, and the cake was washed with water and dried, to obtain acatalyst shown in Table 1. The catalyst was used to conduct a reactionunder the same conditions as in Example 1, to obtain the results shownin Table 2.

EXAMPLE 5

In 50 ml of pure water were dissolved with heating 0.85 g of palladiumchloride, 0.16 g of lead nitrate and 2 g of a 60 wt % aqueous nitricacid solution, then 10 g of a silica-magnesia powder with an averageparticle diameter of 100 μm was added to the solution, and the resultingmixture was stirred. To the mixture was added 50 ml of an aqueoussolution containing 5 wt % of sodium hydroxide and 5 wt % of formalin,the resulting mixture was stirred at 80° C. for 30 minutes, thenfiltered, and the cake was washed with water and dried (solid A). Thesolid A was added to an aqueous solution of 0.72 g of ferric nitratedissolved in 40 ml of pure water and the mixture was stirred. Then 20 mlof a 5 wt % aqueous formalin solution was added to the mixture, theresulting mixture was filtered, and the cake was washed with water andthen dried to obtain a catalyst shown in Table 1. The catalyst was usedto conduct a reaction under the same conditions as in Example 1, toobtain the results shown in Table 2.

EXAMPLE 6

A catalyst was prepared in the same manner as in Example 5 except forusing 0.34 g of zinc acetate in place of ferric nitrate, to obtain acatalyst shown in Table 1. The catalyst was used to conduct a reactionunder the same conditions as in Example 1, to obtain the results shownin Table 2.

EXAMPLE 7

A catalyst was prepared in the same manner as in Example 5 except forusing 0.72 g of ferric nitrate and 0.17 g of zinc acetate in place offerric nitrate, to obtain a catalyst shown in Table 1. The catalyst wasused to conduct a reaction under the same conditions as in Example 1 toobtain the results shown in Table 2.

EXAMPLE 8

In 50 ml of pure water were dissolved with heating 0.85 g of palladiumchloride, 0.16 g of lead nitrate, 0.46 g of bismuth nitrate and 5 g of60 wt % aqueous nitric acid solution, then 10 g of a silica-magnesiapowder with an average particle diameter of 100 μm was added to thesolution, and the resulting mixture was stirred. To the mixture wasadded 80 ml of an aqueous solution containing 5 wt % of sodium hydroxideand 5 wt % of formalin, the resulting mixture was stirred at 70° C. for30 minutes, then filtered, and the resulting cake was washed with waterand dried to obtain a catalyst shown in Table 1. The catalyst was usedto conduct a reaction under the same conditions as in Example 1, toobtain the results shown in Table 2.

EXAMPLE 9

In 50 ml of pure water were dissolved with heating 0.85 g of palladiumchloride, 0.16 g of lead nitrate, 0.46 g of bismuth nitrate and 5 g of a60 wt % aqueous nitric acid solution, then 10 g of a silica-magnesiapowder with an average particle diameter of 100 μm was added to thesolution and the resulting mixture was stirred. To the mixture was added80 ml of an aqueous solution containing 5 wt % of sodium hydroxide and 5wt % of formalin, the resulting mixture was stirred at 70° C. for 30minutes, then filtered, and the resulting cake was washed with water(solid A). The solid A was added to a solution of 0.72 g of ferricnitrate dissolved in 40 ml of pure water and the mixture was stirred.Then 20 ml of a 5 wt % aqueous formalin solution was added to themixture, the resulting mixture was filtered, and the cake was washedwith water and dried to obtain a catalyst shown in Table 1. The catalystwas used to conduct a reaction under the same conditions as in Example 1to obtain the results shown in Table 2.

EXAMPLE 10

A catalyst was prepared in the same manner as in Example 9 except forusing 0.34 g of zinc acetate in place of ferric nitrate, to obtain acatalyst shown in Table 1. The catalyst was used to conduct a reactionunder the same conditions as in Example 1, to obtain the results shownin Table 2.

EXAMPLE 11

A catalyst was prepared in the same manner as in Example 9 except forusing 0.19 g of barium acetate in place of ferric nitrate and using asilica powder with an average particle diameter of 100 μm in place ofsilica-magnesia, to obtain a catalyst shown in Table 1. The catalyst wasused to conduct a reaction under the same conditions as in Example 1 toobtain the results shown in Table 2.

EXAMPLE 12

A catalyst was prepared in the same manner as in Example 9 except forusing 0.42 g of cobalt acetate in place of ferric nitrate and using asilica powder with an average particle diameter of 100 μm in place ofsilica-magnesia, to obtain a catalyst shown in Table 1. The catalyst wasused to conduct a reaction under the same conditions as in Example 1 toobtain the results shown in Table 2.

EXAMPLE 13

A catalyst was prepared in the same manner as in Example 9 except forusing a calcium carbonate powder with an average particle diameter of 6μm in place of silica-magnesia, to obtain a catalyst shown in Table 1.The catalyst was used to conduct a reaction under the same conditions asin Example 1 to obtain the results shown in Table 2.

EXAMPLE 14

A reaction was conducted under the same conditions as in Example 1except for using the catalyst prepared in Example 2 and using 5.02 g ofp-methyl-benzaldehyde as an aldehyde. Methyl p-toluate was obtained as acarboxylic acid ester. The results obtained are shown in Table 2.

EXAMPLE 15

A reaction was conducted under the same conditions as in Example 1except for using the catalyst prepared in Example 2 and using 6.41 g ofp-nitro-benzaldehyde in place of benzaldehyde, to obtain methylp-nitrobenzoate as a carboxylic acid ester. The results thus obtainedare shown in Table 2.

EXAMPLE 16

A reaction was conducted under the same conditions as in Example 1 usingthe catalyst prepared in Example 1 except for using 2.87 g ofmethacrolein in place of benzaldehyde and changing a reaction time to 4hours, to obtain methyl methacrylate as a carboxylic acid ester. Theresults thus obtained are shown in Table 2.

EXAMPLE 17

A reaction was conducted under the same conditions as in Example 1except for using the catalyst prepared in Example 2, using 2.87 g ofmethacrolein in place of benzaldehyde and changing a reaction time to 4hours, to obtain methyl methacrylate as a carboxylic acid ester. Theresults thus obtained are shown in Table 2.

EXAMPLE 18

A reaction was conducted under the same conditions as in Example 1except for using the catalyst prepared in Example 2, using 2.3 g ofacrolein in place of benzaldehyde and changing a reaction time to 4hours, to obtain methyl acrylate as a carboxylic acid ester. The resultsthus obtained are shown in Table 2.

COMPARATIVE EXAMPLE 1

A catalyst was prepared in the same manner as in Example 1 except forusing a titania with an average particle diameter of 100 μm in place ofsilica-magnesia, to obtain a catalyst shown in Table 1. The catalyst wasused to conduct a reaction under the same conditions as in Example 1.The results thus obtained are shown in Table 2.

COMPARATIVE EXAMPLE 2

A catalyst was prepared in the same manner as in Example 2 except forusing a zirconia with an average particle diameter of 50 μm in place ofsilica-magnesia, to obtain a catalyst shown in Table 1. The catalyst wasused to conduct a reaction under the same conditions as in Example 1, toobtain the results shown in Table 2.

TABLE 1 Acid Ammonia chemical Catalyst strength adsorption amountcomposition pKa (μmol/g-cat) Example 1 Pd5—Bi2/SiO2—MgO pKa > 4.8 115.3Example 2 Pd5—Bi2—Fe1/SiO2—MgO pKa > 4.8 128.2 Example 3Pd5—Bi2—Zn1/SiO2—MgO pKa > 4.8 111.7 Example 4 Pd5—Pb1/SiO2—MgO pKa >4.8 130.5 Example 5 Pd5—Pb1—Fe1/SiO2—MgO pKa > 4.8 120.3 Example 6Pd5—Pb1—Zn1/SiO2—MgO pKa > 4.8 106.5 Example 7Pd5—Pb1—Fe1—Zn0.5/SiO2—MgO pKa > 4.8 120.6 Example 8Pd5—Bi2—Pb1/SiO2—MgO pKa > 4.8 121.0 Example 9 Pd5—Bi2—Pb1—Fe1/SiO2—MgOpKa > 4.8 107.6 Example 10 Pd5—Bi2—Pb1—Zn1/SiO2—MgO pKa > 4.8 105.5Example 11 Pd5—Bi2—Pb1—Ba1/SiO2 pKa > 4.8 54.1 Example 12Pd5—Bi2—Pb1—Co1/SiO2 pKa > 4.8 68.1 Example 13 Pd5—Bi2—Pb1—Fe1/CaCO2pKa > 4.8 59.6 Example 14 Pd5—Bi2—Fe1/SiO2—MgO pKa > 4.8 128.2 Example15 Pd5—Bi2—Fe1/SiO2—MgO pKa > 4.8 128.2 Example 16 Pd5—Bi2/SiO2—MgOpKa > 4.8 115.3 Example 17 Pd5—Bi2—Fe1/SiO2—MgO pKa > 4.8 128.2 Example18 Pd5—Bi2—Fe1/SiO2—MgO pKa > 4.8 128.2 Comparative Pd5—Bi2—Fe1/TiO2 4.0< pKa ≦ 4.8 292.8 Example 1 Comparative Pd5—Bi2—Fe1/ZrO2 4.0 < pKa ≦ 4.8177.4 Example 2

TABLE 2 Ester Acetal Conversion selectivity selectivity Yield AldehydeAlcohol (%) (%) (%) (%) Example 1 Benzaldehyde Methanol 91.1 92.5 2.284.3 Example 2 Benzaldehyde Methanol 93.3 95.2 1.2 88.8 Example 3Benzaldehyde Methanol 91.0 93.3 2.5 84.9 Example 4 Benzaldehyde Methanol90.2 92.7 3.2 83.6 Example 5 Benzaldehyde Methanol 90.2 90.8 2.9 81.9Example 6 Benzaldehyde Methanol 87.8 90.3 3.1 79.3 Example 7Benzaldehyde Methanol 90.1 93.5 2.9 84.2 Example 8 Benzaldehyde Methanol93.1 92.6 2.6 86.2 Example 9 Benzaldehyde Methanol 94.3 95.8 1.1 90.3Example 10 Benzaldehyde Methanol 93.3 94.5 1.5 88.2 Example 11Benzaldehyde Methanol 91.5 93.6 1.3 85.6 Example 12 BenzaldehydeMethanol 94.1 94.2 1.0 88.6 Example 13 Benzaldehyde Methanol 89.1 92.82.0 82.7 Example 14 p-Methylbenzaldehyde Methanol 97.8 93.7 2.1 91.6Example 15 p-Nitrobenzaldehyde Methanol 69.0 90.8 3.5 62.7 Example 16Methacrolein Methanol 88.0 96.8 0.31 85.2 Example 17 MethacroleinMethanol 85.0 95.7 0.53 81.3 Example 18 Acrolein Methanol 95.0 96.3 0.4291.5 Comparative Benzaldehyde Methanol 97.2 0 98.0 0 Example 1Comparative Benzaldehyde Methanol 92.9 0 90.8 0 Example 2

INDUSTRIAL APPLICABILITY

According to the process of the present invention, carboxylic acidesters can be produced with a high yield from aldehydes and alcohols.

What is claimed is:
 1. A process for producing a carboxylic acid ester,comprising: reacting an aldehyde and an alcohol in a liquid phase in thepresence of molecular oxygen in the presence of a catalyst comprising atleast palladium and an element X, wherein X is bismuth, lead or acombination thereof, supported on a carrier selected from the groupconsisting of calcium carbonate, silica and silica-magnesia, wherein thecatalyst has an acid strength, pKa, of more than 4.8 and shows anammonia chemical adsorption amount at 0° C. of 0-150 μmol/g-catalyst. 2.The process according to claim 1 wherein the alcohol is methanol,ethanol, isopropanol, allyl alcohol, methallyl alcohol, or a mixturethereof.
 3. The process according to claim 1 wherein the alcohol ismethanol.
 4. The process according to claim 1 wherein the aldehyde isbenzaldehyde, methylbenzaldehyde, nitrobenzaldehyde, acetaldehyde,propionaldehyde, isobutyl aldehyde, acrolein, methacrolein,crotonaldehyde, or a mixture thereof.
 5. The process according to claim1 wherein the aldehyde is benzaldehyde, methylbenzaldehyde,nitrobenzaldehyde, acrolein, methacrolein, or a mixture thereof.
 6. Theprocess according to claim 1 wherein the ammonia chemical adsorptionamount is 30-140 μmol/g-catalyst.
 7. The process according to claim 1,wherein said ammonia chemical absorption amount is 30-140μmol/g-catalyst.
 8. The process according to claim 1, wherein the saidaldehyde and alcohol react in a molar ratio ranging from 1:100 to 1:1.9. The process according to claim 1, wherein the reaction is conductedat a temperature ranging from 0-100° C.
 10. The process according toclaim 1, wherein the amount of molecular oxygen in the reaction rangesfrom 10-500 ml/min per 100 ml of reaction liquid.
 11. The processaccording to claim 1, wherein the carrier has an average particlediameter and a specific surface area of 5-150 μm and 50-200 m²/g,respectively.
 12. The process according to claim 1, wherein the amountsof catalytically active components of the catalyst, based on 100 partsby wt of the carrier, range from 1-15 parts by wt of Pd and from 0.1-15parts by wt of element X.